Sil-alkyd coatings for wire

ABSTRACT

A MODIFIED POLYESTER RESIN COATING FOR MAGNET WIRE OR THE LIKE MADE BY REACTING (A) TEREPHTHALIC, ISOPHTHALIC ACID OR DIMETHYL ESTERS THEREOF, (B) A POLYHYDRIC ALCOHOL, AND (C) A SILANE OR A LOW MOLECULAR WEIGHT, PARTIALLY CONDENSED, PHENYL, METHYL, METHYL ALKYL OR PHENYLMETHYL POLYSILOXANE CONTAINING AT LEAST ONE REACTIVE OH GROUP BONDED TO THE SILICON ATOM. THE SILICON CONTAINING COMPOUNDS REACTS WITH THE (A) COMPONENT, OR IF IT CONTAINS A REACTIVE COOH GROUP, WITH THE (B) COMPONENT. THESE POLYESTER RESINS ARE CHARACTERIZED BY A REMARKABLY LOW COEFFICIENTS OF FRICTION AND MAY BE USED AS A WIRE &#34;ENAMEL&#34; WITH OR WITHOUT AN OVERCOAT.

United States Patent 3,583,885 SIL-ALKYD COATINGS FOR WIRE Jerome A. Preston, Fort Wayne, Ind., assignor to Essex International, Inc. No Drawing. Filed Aug. 29, 1969, Ser. No. 854,285 Int. Cl. H01b 3/42; C08g 31/06, 31/32 US. Cl. 117-218 6 Claims ABSTRACT OF THE DISCLOSURE A modified polyester resin coating for magnet wire or the like made by reacting (a) terephthalic, isophthalic acid or dimethyl esters thereof, (b) a polyhydric alcohol, and (c) a silane or a low molecular weight, partially condensed, phenyl, methyl, methyl alkyl or phenylmethyl polysiloxane containing at least one reactive OH group bonded to the silicon atom. The silicon containing compound reacts with the (a) component, or if it contains a reactive COOH group, with the (b) component. These polyester resins are characterized by a remarkably low coefiicient of friction and may be used as a wire enamel with or without an overcoat.

BACKGROUND OF THE INVENTION This invention relates to an improved magnet wire having a resinous coating characterized by a low coefficient of friction due to the composition of the coating. Magnet wire having such insulating coatings are used in winding electrical coils for use in relays, solenoids and the like. The wire is wound at high speeds and to reduce friction it has been customary heretofore to apply oil to the wire. After the coil has been wound, it is customary to varnish the entire assembly by dipping it in varnish. However, the varnish will not adhere well to the wire which has been oiled and consequently, the wound bobbins must be degreased before varnishing.

The primary object of this invention is to provide a Class B (130 C.) or higher magnet wire which requires no oil for Winding. Wire prepared using the compositions disclosed herein has a significantly superior dry lubricity with an oil free surface. The slippery nature of the surface does not prevent varnish from adhering to the coating. Consequently, better varnish coverage, spray and/ or dipping techniques are possible. Encapsulation of bobbins is also facilitated because there is no trapped oil in coils wound with wire in accordance with this invention.

Another object is to provide improved polyester coatings for electrical conductors.

A further object is to provide wire enamels which exhibit exceptionally good resistance to heat aging.

Still further objects and the entire scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

A further object of the invention is to provide a significantly superior dry lubricity with an oil free surface. There are significant advantages in this invention; it provides for cleaner winding, therefore, cleaner shop and material storage areas because dust and dirt will not collect as readily, and no oil can be thrown from the Wire or burned due to heat developed from friction. Further advantage is realized by the efficiency of polysiloxane modified polymers in providing improved space utilization. This results in wound units with reduced mean turn lengths.

Therefore, a given unit can be wound with less wire.

3,583,885 Patented June 8, 1971 The coeflicient of friction obtained on any insulation is primarily due to the material used for the outer coating and can be affected to a limited degree through the use of spooling oils or other topical lubricants. For nylon over-coated insulations, the coefficient of friction is approximately 0.17 using a polished steel block sliding on coated wire. Other commonly used films range up to 0.33. The modified series, regardless of the insulation type, consistently measures 0.17 or below.

Although the industry has established the windability characteristics of the commercially available insulations, both magnet wire users and suppliers alike have rightfully maintained that spooling oil on the wire has been a necessity. For the users, this practice has improved dereeling. For producers, it has enabled them to meet packaging and weight requirements. However, this oiling practice has required rigid controls regarding the type and quantity of oil used. If a high grade mineral oil is not used, the underlying film can be adversely affected. It is likewise well known that excess oil causes the oil to be thrown in all directions from a winding machine, and often interferes with taping operations. On the other hand, too little oil results in oversize coils causing winding operators to increase winding tensions which often stretch the conductor, and work-harden the wire. This again adversely affects the winding, nesting of the Wire, and subsequent space fill.

Since the polysiloxane modified polymer films of my invention exhibit a very low friction coefficient, and since this characteristic is uniform around and along the entire length of wire, the use of lubricants is no longer necessary. This uniformity permits parts to freely rotate and reduce loading of bearings and bushings. Additional insulations, such as slot wedges, can be more easily placed in units wound from polysiloxane modified resin coatings because of the improved space factors.

Work hardening of metal conductors is a problem in winding magnet wire, while wire coated with polysiloxane modified resin solutions reduces this problem because high winding tensions are not needed. Forming operations are minimized and forming procedures on conductors are equalized because this invention allows wires to slide past one another when formed. Coil windings made from wire coated according to this invention require less effort to seat and insert in various forming devices.

Taping of coils wound with wire made from this invention is more readily accomplished since tapes will stick to this wire and no oil removal procedures are necessary. Consequently, no oil removal or cleaning units are necessary. Better varnish coverage, spray and/ or dipping techniques, is accomplished since no oil is present to interfere with the wettability of the varnish, enamel and/or paint.

Many current encapsulants for wound units are plagued by entrapped air and/ or oil left on wire by conventional wire operations. Encapsulation, thus, is improved because no trapped oil is present in units made from this invention. Because polysiloxane modified resins have a lower coefficient of friction, wire made with these coatings reduces the winding, forming and handling damage normally encountered by conventional wires.

The unique wire coating of this invention is prepared from modified polyester resins in which a siloxane is added as part of the polyhydric alcohol constituent or as a partial dibasic acid substitute when the resin is being prepared. In such coatings, I prefer to use organo siloxanes which have at least one and preferably two or three terminal OH, H, or COOH groups. The OH and H react with the acid component of the polyester. The COOH groups react as an acid with polyols. The polyhydric alcohol portion of the polyester consists of 20-50 equivalent percent ethylene glycol and 2-40 equivalent percent of a saturated aliphatic polyhydric alcohol having three OH groups, which latter alcohol contains from 0.5 to 25% of a siloxane. The ratio of alcohol to acid (OH to COOH or COOCH will range from 4:1 to less than 1:1. The preferred siloxane is a low molecular weight, partially condensed phenyl, methyl, methyl alkyl or phenylmethyl polysiloxane containing at least one reactive OH group bonded to a silicon atom. It may be represented as follows:

in which R is CH phenyl, OH, H, or carboxyalkyl or alkyl and R is CH or phenyl, carboxyalkyl, alkyl, and n=2 to 20 or more, or the organosilicon compounds represented by the following formula may be substituted:

where R is an alkyl radical of less than carbon atoms or a phenyl radical, X is an alkoxy, aryloxy or OH radical, m has an average value of from 1 to 2, n has an average value of from .01 to 3, and the sum of (m+n) is not greater than 4. The above organosilicon compounds include both monomeric alkoxy-silanes and silanols of the formula R SiX and partial condensates thereof. These partial condensates are polymeric siloXanes having hydrocarbon groups, alkoxy groups and/or OH radicals attached to the silicon. The number of functional (1.e. X) groups per silicon may vary from 1 functional group per 100 silicons to 3 functional groups per silicon. Both the above silanes and the partial condensates are known mate rials.

The hydrocarbon groups may be alkyl radicals such as methyl, ethyl, propyl, butyl, or phenyl radicals. Any a lkoxy groups may be present in the silanes although 1t 1s preferred that the alkoxy radicals contaln less than 5 carbon atoms, since the corresponding alcohols are more easily removed from reaction mixtures.

Specific silanes which may be employed in this invention are, for example, phenylmethyldiethoxysilane, phenyltrimethoxysilane, dimethyldiisopropoxysilane, diethyldibutoxysilane, monomethyltriisopropoxysilane, diphenylsilanediol, phenylmethylsilanediol and diethylsila-nediol. It is understood that either individual silanes or mixtures of one or more silanes may be employed together with partial condensates of individual silanes or mixed silanes. These partial condensates are the preferred starting materials.

The saturated aliphatic polyhydric alcohols suitable for use in these particular compositions are trimethylolpropane, trimethylolethane, 1,3-butylene glycol, 1,2-butylene glycol, 1,4-butylene glycol, trishydroxyethylisocyanurate, trimethylolbutane, pentaerythritol, sorbitol, mannitol, glycerine, ethylene glycol, neopentyl glycol, and propylene glycol.

When dissolved in suitable solvents and catalyzed and applied to wire in standard wire coating ovens, the resins of my invention result in smooth coatings. While polyester silicone resins can cure without additional catalysis, it is desirable to insure more complete cure by adding as a catalyst to a solution of the resin in various solvents, carboxylic acid salts of various metals, organic titanates and aromatic and aliphatic isocyanates are satisfactory catalysts. Generally, the level used may be as little as 0.1% to 20% by weight, based on total resin solids in the solution. Specific examples of satisfactory catalysts are zinc octoate, tetrakis (Z-ethylhexyl titanate), titanium acetyl acetonate, tetrabutyl titanate and cobalt'octoate.

The polymers prepared in this invention are suitable for use'as magnet wire enamels. All passed'Class C. NEMA requirement. Several are Class 180 C. NEMA or above. The degree of reduced coefficient of friction depends upon thenature of the resin which has. been. modified. a I

Some wires base-coated with polyester siloxane resins of the type described had improved resistance to burn out, moisture and voltage endurance. The exten't ofthe' improvement depends in part upon the overcoat used over the polyester base coat.

It is not always practical to overcoat magnet wire in very fine diameters. Fine magnet wire coated with solutions of these polymers provide satisfactory electrical and thermal properties without a topcoat. Unlike fine wire having a conventionalenamel coating,-the wirehaving my improved resin coating need not be lubricated with oil, and therefore, a topcoat can be applied without any spe cial treatment, if desired.

Polyester siloxane resins prepared from a mixture of ingredients having a composition range within the scope of this invention are completely satisfactory for use as magnet wire insulation and slot insulation at temperatures of at least C. for continuous operation. The suitability of these enameled wires for high temperature magnet wire applications is indicated by the fact that these wires pass all NEMA standard tests for temperature classifications through 155 C.

Several conductors coated with resins prepared in accordance with this invention have a class C. thermal rating by the ASTM D 2037 procedure. The coated conduetors exhibit reduced coefiicients of friction over normally prepared polyesters even when topcoated. Polyesters prepared without siloxane modification have friction coefficients as high as 0.33, while the resins prepared in accordance with this invention ranged from 0.17 to as low as 0.095, depending on formulation. Some of these polymers had increased voltage endurance, resistance to moisture, and increased burn out resistance.

The following examples are illustrative of the invention:

v Example l The following ingredients were placed in a'four-necked reaction vessel with stirrer, thermometer, inert gas bleed, and a heated condenser:

Ingredients: 'Parts by weight Dimethyl terephthalate 4 6 -Ethylene-glycol 31 Trimethylol propane 23 Diphenylsilanediol 2.3 Zinc acetate 0.08

(Sufiicient xylene or other solvent for azeotropic distillation.)

The reaction products are heated to 130 C. in 30 minutes. The zinc acetate catalyst is added and the temperature raised to 240 C. and held for 3 hours. The temperature is then raised to 250 C. with viscosity determination used to indicate termination of the reaction. This period is approximately /2 hour. The reaction is then stopped and the resin quenched with cresylic acid. The resin is then diluted to 33% solids in orthocresol and orthochlorophenol and applied to wire in multiple layers as a base coat. The wire was cured after each pass through the solution at a temperature of 275 C. to 475 C. in a vertical tower. The resultant product was found to be useful as a Class H magnet wire.

The coeflicient of friction of wire coated with the above polymer was 0.15. Polyesters of this type containing no silicone were found to have a coeflicient" of friction on wire of 0.33. Neither wire was overcoated. Cut thru was 380 C. for Example #1 and 360 C. for a convention class H polyester. Both wires were overcoated with 2 coats of Amide Imide A I-537 enamel made by Amoco Chemical Corporation for the cut thru test.

Example 2 Another coating was prepared as indicated in Example 1 using the following compositioni Ingredients: Parts by weight Dimethyl terephthalate 34.0 Dimethyl isophthalate 34.0 Ethylene glycol 13.55 Diphenylsilanediol 23.65 Glycerine 2.58 Titanium acetyl acetonate (alcoholysis catalyst) 8.75

Suificient xylene for azeotropic distillation.

The coeflicient of friction was 0.14 when 6 coats of the above polymer as a 32% solids enamel in 55 parts ortho cresol and 45 parts of an aromatic hydrocarbon blend was applied to wire as in Example 1.

Example 3 Another coating was prepared as indicated in Example 1 using the following composition:

Ingredients: Parts by weight Dimethyl terephthalate 460 Ethylene glycol 210 Trishydroxy ethyl isocyanurate 200 Trimethylol propane 130 Diphenylsilanediol 23 Zinc acetate 0.08

(Suflicient xylene or other solvent for azeotropic distillation.)

Wire coated enamel made using this polymer had a coefiicient of friction of 0.14 when cured on AWG 18 copper wire in 6 passes with no topcoat. Cut thru with four coats of the above polymer (30% solids in a blend of 55 parts of ortho cresol and 45 parts of an aromatic hydrocarbon and 2 coats of Amide Imide AI-537 topcoat was 450 C. compared to 360 C. for a conventional class H polyester.

Example 4 Another coating resin was prepared in equipment as described in Example 1 using the following composition and technique:

Ingredients: Parts by weight Dimethyl terephthalate 1380 Ethylene glycol 560 Glycerine 360 Carboxyethylpolydimethylsiloxane 57.5 Litharge 0.2

and the range of proportions useful for the purposes of this invention.

-'- Operable range in percent Typical formula of total Material solids No. 1 No. 3 No. 4

Isophthalie acid 0. 5-3

0. 5-50 0. 5-50 Dimethyl isophthalata. 0. 5-20 Ethylene glycol 0. 5-45 Neopentyl glycol 0. 5-45 Trimethylolpropane. 0. 5-45 Trimethylolethane. 0. 5-45 1,3-butylene glycol 0. 5-- 1,2-butylene glycol. 0. 5-25 1,4-butlyene glycol 0. 5-25 Trishydroxyethylisoeyanm'ate 0. 5-45 Trimethylolbutane. 0. 5-25 Glycerine 0. 5-45 Diphenylsilanediol 2. 3-35 Phenylpropylcyclohydroxy oxane. 5. 0-35 Hydroxy terminated copolymers of polyoxy alkylene ether and dimethyl polysiloxane 0. 5-35 Carboxyalkyl terminated polydimethylsiloxane 0. 05-20 What is claimed is:

1. A modified polyester resin having properties of improved dry lubricity characterized by loW coefficient of friction comprising the cured reaction product of:

(a) an acid component selected from the group consisting of terephthalic acid, isophthalic acid, dimethyl esters thereof, and mixtures thereof,

(b) polyhydroxy components including (1) ethylene glycol,

(2) trishydroxyethyl cyanurate, and

(3) a polyhydric alcohol selected from the group consisting of trimethylolpropane, trimethylolethane, 1,3 butylene glycol, 1,2 butylene glycol, trimethylolbutane, pentaerythritol, sorbitol, mannitol, glycerine, neopentylglycol, propylene glycol and mixtures thereof, and

(c) an organo-silicon component, the compounds of which contain at least one terminal OH, alkoxy or COOH group,

said organo-silicon component compound being selected from the group consisting of phenylmethyldiethoxysilane, phenyltrimethoxysilane, dimethyldiisopropoxysilane, diethyldibutoxysilane, monomethyltriisopropoxysilane, diphenylsilanediol, phenylmethylsilanediol, diethylsilanediol, carboxyethylpolydimethylsiloxane, and mixtures thereof,

said organo-silicon component functioning as a partial polyhydric alcohol constituent in said polyester when said terminal groups are selected from OH or alkoxy groups, and functioning as a partial acid component when said terminal groups are COOH groups,

the ratio of total alcohol, taken as OH groups, to acid groups, taken as COOH or COOCH groups, being present in said components in the range of from about 4:1 to less than about 1:1.

2. In an insulated conductor having a metal core and an insulating resin coating, the improvement in said conductor consisting of the resin coating as set forth in claim 1, said conductor being characterized by an imprloved dry lubricity that obviates the need for lubrication o1 3. The conductor of claim 2 having an overcoat of amide-imide resin applied to said insulating resin coating.

4. The conductor of claim 2 in which the alcohol is glycerine, and the organo-silicon compound is diphenylsilanediol.

7 5. The conductor of claim 2 in which the polyhydric alcohol is trimethylolpropane and the organo-silicon compound is diphenylsilanediol.

6. The conductor of claim 2 in which the polybasic acid is dimethyl terephthalate, the alcohol is glycerine, and the organo-silicon component acting as an acid is carboxyethylpolydimethylsiloxane.

References Cited UNITED STATES PATENTS 2,686,739 8/1954 Kohl 260824 2,686,740 8/1954 Goodwin 260824 8 1/1958 Edelman et a1. 260824 7/1958 Shor 260-827 7/ 1962 Saville 260824 7/1962 Modic et a1 260824 6/1969 Giilitz et a1 260824 FOREIGN PATENTS 1/1959 Canada Y 260824 10 SAMUEL H. BLECH, Primary Examiner US. Cl. X.R. 

